Defects in integrated circuits are traced often to electrical shorts in metallization. A common metallization fault occurs between first and second metallization levels and is attributable to the sharp step on conductor rails of the first level over which a portion of the second level traverses. Various techniques for tapering the edges of the first level metallization have been proposed. Several of these depend on developing a faster etch rate at the surface of the first level metal layer than at the bottom. This can be achieved by varying the composition of the layer as it is deposited, or by damaging the surface of the layer after it has been deposited. As the layer is etched to define the metallization pattern, etching proceeds laterally at the surface at an enhanced rate and the final profile at the edge of the masked portion is tapered or curved. The insulating layer that is then deposited follows the curved topology, so the second level metal, where it crosses the first, sees a gradual rather than abrupt step.
According to this invention a simpler and more direct method is used to obtain a rounded corner on first level metallization. It is based on the recognition that metals used for metallization can be melted and quenched in a period so short that surface tension acts on the shape of the metal, but flow does not occur. The result is that the metallization pattern remains intact but the upper corners or other sharp features of the pattern are rounded.
Techniques superficially similar to this have been applied to glass articles for centuries. However, these are known to rely on the fact that glass does not have a sharp melting transition, and the rounded effects are regarded as due to slight flow of the glass. Surface tension is incidental.
It has also been found that the conductivity of polysilicon metallization can be increased by the technique of the invention.